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SDIRSACR Oncology Insights

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From Tumor Suppression to Stress Response: The Diverse Roles of Sirtuin 3 in Cancer and Sex-Dependent
DNA Damage Adaptation

Kate Šešelja1, Robert Belužić1, Ena Šimunić1, Iva I. Podgorski1, Marija Pinterić1, Marijana Popović Hadžija1, Tihomir
Balog1, Hansjorg Habisch2, Tobias Madl3, Aleksandra Korać4 and Sandra Sobočanec1

1Laboratory for Metabolism and Aging, Division of Molecular Medicine, Ruđer Bošković Institute, 10000 Zagreb, Croatia
2Division of Medicinal Chemistry, Medical University of Graz, Neue Stiftingtalstraße 6, Graz 8010, Austria
3BioTechMed Graz, Mozartgasse 12/II, Graz 8010, Austria
4Faculty of Biology, University of Belgrade, Studentski trg 16, Beograd 11158, Serbia

Keywords: Sirtuin 3, breast neoplasms, tumor suppressor proteins, DNA damage, sex factors

Background: Sirtuin 3 (Sirt3), a mitochondrial NAD⁺-dependent deacetylase, regulates mitochondrial metabolism,
oxidative stress, and cell survival. Its context-dependent role spans from functioning as a tumor suppression in estrogen-
sensitive and triple-negative breast cancer (TNBC) to facilitating stress adaptation in non-transformed cells. However,
the mechanisms through which Sirt3 modulates cell fate across various conditions remain incompletely understood.

Materials and Methods: To investigate the role of Sirt3 in cancer and stress response, we used MCF-7 (ER-α⁺) and
MDA-MB-231 (TNBC) breast cancer cells stably transfected with Sirt3 or control vectors. Assays included Western
blotting, qPCR, flow cytometry, metabolic activity, mitochondrial function, and colony formation. Confocal microscopy
and immunocytochemistry assessed protein localization. Separately, primary male and female mouse embryonic
fibroblasts (MEFs) with or without Sirt3 were exposed to etoposide-induced DNA damage to evaluate sex-specific
stress responses.
Results: in MCF-7 cells, Sirt3 overexpression reduced estrogen-induced proliferation, colony formation, and
S-phase progression by stabilizing p53 and disrupting its interaction with ER-α. This was accompanied by increased
oxidative phosphorylation and a metabolic shift unfavorable for tumor growth. In MDA-MB-231 cells, Sirt3 enhanced
mitochondrial biogenesis, ROS, and metabolic activity, but also elevated DNA damage, apoptosis, and the formation of
multinucleated cells. In MEFs, Sirt3 loss led to sex-specific responses to DNA damage with male cells showing relative
resistance, whereas female cells exhibited increased sensitivity and impaired stress adaptation.
Conclusion: Sirt3 acts as a tumor suppressor in ER-α⁺ and TNBC models by modulating mitochondrial metabolism and
cellular stress responses. Its depletion causes DNA damage responses in a sex-dependent manner, emphasizing its role
not only in cancer biology but also in aging and cellular senescence. These findings highlight the therapeutic potential
of targeting Sirt3 in both cancer and age-associated disorders.

Acknowledgments and funding: This study was funded by the Croatian Science Foundation (HrZZ), grant number IP-
2022-10-4806.

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